Classic Load Balancer (CLB) improves the throughput of applications by distributing requests to different backend servers. CLB can also improve the availability of applications because it can prevent single points of failure (SPOFs). To use CLB, you must create a CLB instance and add listeners and backend servers to the CLB instance. Alibaba Cloud provides both Internet- and internal-facing CLB instances. If you choose the pay-by-specification metering method, high-performance instances and shared-resource instances are supported.
Instance status
Instance status | Status description | Why the CLB instance is locked | Whether the CLB instance can be deleted | Whether configurations can be changed |
Running | The CLB instance is running as expected. | N/A | Based on whether delete protection is enabled.
| Based on whether the configuration read-only mode is enabled.
|
Locked | The CLB instance is locked. | Locked (Overdue Payment): The CLB instance is locked due to overdue payments. Renew your CLB instance at the earliest opportunity. The CLB instance resumes after it is unlocked. | No | No |
Locked (Security Risks): The CLB instance is locked due to security risks. You can go to the Penalties List page in the Security Control console to apply for unlocking. | No | |||
Stopped | The CLB instance is stopped. | N/A | Yes | No |
Network types
Alibaba Cloud provides both Internet- and internal-facing CLB instances.
Internet-facing CLB instances
When you create an Internet-facing CLB instance, it is assigned a public IP address. You can associate your domain name with the public IP address. Internet-facing CLB instances receive requests from clients over the Internet and forward requests to backend servers based on the forwarding rules that you configure for listeners.
Internet-facing CLB instances have the following features:
Each Internet-facing CLB instance is assigned a public IP address. You cannot disassociate the public IP address from the CLB instance.
Pay-as-you-go CLB instances support the pay-by-bandwidth and pay-by-data-transfer metering methods.
Internal-facing CLB instances
Internal-facing CLB instances provide external services by using private IP addresses. Requests from the internal network of Alibaba Cloud are distributed to backend servers based on the forwarding rules that you configure for listeners.
You can associate elastic IP addresses (EIPs) with internal-facing CLB instances to provide Internet-facing services. Internal-facing CLB instances provide the following capabilities to support Internet access:
You can associate EIPs with internal-facing CLB instances and disassociate EIPs from internal-facing CLB instances based on your business requirements.
You can add EIPs to an Internet Shared Bandwidth instance to reduce Internet costs.
Internal-facing CLB instances support only VPCs.
The private IP address of an internal-facing CLB instance is assigned from the CIDR block of a vSwitch in the VPC that you specify. The CLB instance is accessible only from Elastic Compute Service (ECS) instances in the VPC.
Instance specifications
The pay-by-specification billing method supports high-performance CLB instances and shared-resource CLB instances.
High-performance CLB instances provide reliable performance, while shared-resource CLB instances share resources with each other without guaranteed performance for each instance.
The CLB instances you created before Alibaba Cloud launched high-performance CLB instances are all shared-resource CLB instances. You can view the instance type in the CLB console.
Shared-resource CLB instances are no longer available for purchase.
High-performance CLB instances
The key metrics of high-performance CLB instances are described as follows:
Maximum number of connections
The maximum number of concurrent connections that a CLB instance supports. If the number of existing concurrent connections reaches the upper limit, new connection requests are dropped.
CPS
The number of new connections that can be established per second. If CPS reaches the upper limit, new connection requests are dropped.
QPS
The number of HTTP or HTTPS queries (requests) that can be processed per second. This metric is specific to Layer 7 listeners. If QPS reaches the upper limit, new query requests are dropped.
The following table describes the specifications of high-performance CLB instances provided by Alibaba Cloud. The specifications on the buy page of CLB instances shall prevail.
Table 1. Specifications of high-performance CLB instances
Specification | Maximum number of connections | Connections per second (CPS) | Queries per second (QPS) |
Small I (slb.s1.small) | 5,000 | 3,000 | 1,000 |
Medium I (slb.s2.small) | 50,000 | 5,000 | 5,000 |
Medium II (slb.s2.medium) | 100,000 | 10,000 | 10,000 |
Large I (slb.s3.small) | 200,000 | 20,000 | 20,000 |
Large II (slb.s3.medium) | 500,000 | 50,000 | 30,000 |
Super Large I (slb.s3.large) | 1,000,000 | 100,000 | 50,000 |
The maximum capacity of a pay-by-LCU CLB instance is the same as that of a Super Large I (slb.s3.large) CLB instance.
If you require more connections at Layer 4, use Network Load Balancer (NLB). If you require higher QPS at Layer 7, use Application Load Balancer (ALB).
For more information on NLB, see What is NLB?
For more information on ALB, see What is ALB?
Shared-resource CLB instances
The following table describes the features of shared-resource CLB instances provided by Alibaba Cloud.
The following table provides FAQs on shared-resource CLB instances.
Question | Answer |
Can I purchase shared-resource CLB instances? | No, they are no longer available for purchase. |
Do shared-resource CLB instances provide different specifications? | The performance of shared-resource CLB instances is not guaranteed. Therefore, you cannot choose the specification of a shared-resource CLB instance. |
Am I charged specification fees for existing shared-resource CLB instances? | No, you are not. You are charged specification fees only if you upgrade the shared-resource CLB instances to high-performance ones. After the free trial for high-performance CLB instances ends, you are charged specification fees if you continue to use the high-performance CLB instances. |
Can I upgrade a shared-resource CLB instance to a high-performance one? | Yes, you can.
|
Differences between high-performance and shared-resource CLB instances
In the following table, a check mark (✓) indicates that a feature is supported, while a cross (×) indicates that a feature is not supported.
Item | High-performance CLB instance | Shared-resource CLB instance |
Resource allocation | Exclusive resources | Shared resources |
Service uptime guaranteed by terms of service level agreement (SLA) | 99.95% | Not supported |
IPv6 | ✓ | × |
Server Name Indication (SNI) for multiple certificates | ✓ | × |
Blacklists and whitelists | ✓ | × |
Association with elastic network interfaces (ENIs) | ✓ | × |
Adding backend servers by specifying the secondary IP addresses of ENIs attached to ECS instances | ✓ | × |
HTTP-to-HTTPS redirection | ✓ | × |
Consistent hashing | ✓ | × |
TLS security policies | ✓ | × |
HTTP2 | ✓ | × |
WebSocket or WebSocket Secure | ✓ | × |
IP version
IPv4 and IPv6
CLB instances support both IPv4 and IPv6. When creating a CLB instance, specify the IP Version parameter. The following table describes the valid values of the parameter.
IP Version | Default configuration | Description |
IPv4 |
| If you set IP Version to IPv4, only clients using IPv4 addresses such as 192.168.0.1, can access your CLB instance. |
IPv6 |
| If you set IP Version to IPv6, only clients using IPv6 addresses such as 2001:db8:1:1:1:1:1:1, can access your CLB instance. |
Features and limitations of IPv6 CLB instances
Features
Switch from IPv4 to IPv6 without service interruptions
IPv6 CLB instances support backend servers that use IPv4 addresses. You can migrate services to IPv6 CLB instances without changes to existing systems.
When network traffic increases, you can add an IPv6 gateway to your CLB instance and scale out backend servers without impacting your IPv4 services.
Secure and reliable workload deployment
You can configure a blacklist for CLB to block network traffic from malicious IP addresses.
You can also configure a whitelist for CLB to allow network traffic only from specified IP addresses.
Limitations
Only Internet-facing CLB instances support IPv6.
For regions where IPv6 CLB instances are supported, see Regions in which CLB is available.
IPv6 packets have longer IP headers than IPv4 packets. When an IPv6 CLB instance uses a UDP listener, ensure that the following requirement is met: The maximum transmission unit (MTU) supported by the elastic network interface (ENI) that each backend server uses to communicate with CLB does not exceed 1,200 bytes. Otherwise, oversized packets may be discarded. You must modify the MTU setting in the configuration files of some applications accordingly. TCP supports the Maximum Segment Size (MSS) announcement. You do not need to modify the configurations of applications if a CLB instance uses a TCP listener.
References
For more concurrent connections at Layer 4, use NLB. For a higher QPS value at Layer 7, use ALB.
For more information about NLB, see What is NLB?
For more information about ALB, see What is ALB?
For more information about selecting the specification of a high-performance CLB instance, see FAQs about CLB instances.